LED emissive display device and method for producing such a device

ABSTRACT

A display device including a first integrated circuit including: an assembly of light-emitting diodes, each diode including a vertical stack of a first semiconductor layer of a first conductivity type and of a second semiconductor layer of a second conductivity type; and on the side of a surface of the first circuit opposite to the first semiconductor layer, a connection structure including a dielectric layer having a plurality of identical or similar connection pads, regularly distributed across the entire surface of the first circuit, arranged therein, each diode having a first electrode in contact with at least one pad of the connection structure, and a second electrode in contact with a plurality of pads of the connection structure at the periphery of the plurality of diodes.

This application is a national stage filing under 35 U.S.C. § 371 ofInternational Patent Application Serial No. PCT/FR2019/050608, filedMar. 18, 2019, which claims priority to French patent applicationFR18/52465. The entire contents of these applications are incorporatedherein by reference in their entireties.

BACKGROUND

The present application relates to the field of optoelectronic devices.

It more particularly concerns an emissive display device comprisinglight-emitting diodes (LEDs), also called micro LED display, and amethod of manufacturing such a device.

DISCUSSION OF THE RELATED ART

An emissive display device comprising an assembly of a plurality ofLEDs, for example made of gallium nitride, and a control circuitenabling to individually control the LEDs in order to display images,have already been provided.

The case where the control circuit is integrated inside and on top of asemiconductor substrate, for example, a silicon substrate, for example,in CMOS technology, is here more particularly considered.

To form such a device, it may be provided to separately manufacture thecontrol circuit and the LED assembly, and then to connect them to eachother to form the display device. On the side of one of its surfaces,the control circuit comprises a plurality of metal pads, each pad beingintended to be connected to an electrode of a LED of the LED assembly,to be able to individually control the LEDs. The LED assembly is forexample monolithically formed on a support substrate, and thentransferred onto the control circuit so that each LED has an electrode(anode or cathode) connected to one of the metal pads of the controlcircuit.

An issue lies in the need to accurately align the control circuit andthe LED assembly during the step of assembly of the two elements, sothat each LED is effectively positioned on the metal pad correspondingthereto in the control circuit. Such an alignment is particularlydifficult to achieve when the pitch between pixels decreases, and is anobstacle to an increase in the resolution and/or in the integrationdensity of the pixels.

SUMMARY

Thus, an embodiment provides a display device comprising a firstintegrated circuit comprising:

an assembly of a plurality of light-emitting diodes, each diodecomprising a vertical stack of a first semiconductor layer of a firstconductivity type and of a second semiconductor layer of the secondconductivity type, and the diodes being separated from one another bytrenches;

for each diode, a first electrode arranged on top of and in contact withthe surface of the second layer opposite to the first layer;

a second electrode common to said plurality of diodes, the secondelectrode extending in the trenches and at the periphery of theplurality of diodes and being in contact, in each diode, with the firstsemiconductor layer; and

on the side of a surface of the first circuit opposite to the firstsemiconductor layer, a connection structure comprising a dielectriclayer having a plurality of identical or similar connection pads,regularly distributed across the entire surface of the first circuit,arranged therein, each diode having its first electrode in contact withat least one pad of the connection structure, and the second electrodebeing in contact with a plurality of pads of the connection structure atthe periphery of the plurality of diodes.

According to an embodiment, the device further comprises a secondintegrated circuit formed inside and on top of a semiconductorsubstrate, the second circuit comprising, for each diode of the firstcircuit, a metal pad intended to be connected to the first electrode ofthe diode, and a metal electrode intended to be connected to the secondelectrode of the first circuit.

According to an embodiment, the first and second circuits are bonded toeach other by direct hybrid bonding so that each first electrode of thefirst circuit is electrically connected to a metal pad of the secondcircuit, and so that the second electrode of the first circuit iselectrically connected to the electrode of the second circuit.

According to an embodiment, the second circuit comprises a connectionstructure comprising a dielectric layer having a plurality of identicalor similar connection pads, regularly distributed across the entiresurface of the second circuit, arranged therein, each metal pad of thesecond circuit being in contact with at least one connection pad of theconnection structure of the second circuit, and the electrode of thesecond circuit being in contact with a plurality of connection pads ofthe connection structure of the second circuit in a peripheral region ofthe electrode of the second circuit.

According to an embodiment, the second circuit comprises, for each metalpad of the second circuit, an elementary control cell comprising one ora plurality of transistors, enabling to control the current flowingthrough the corresponding diode of the first circuit and/or a voltageapplied across the corresponding diode of the first circuit.

According to an embodiment, the second circuit is made in CMOStechnology.

According to an embodiment, the diodes of the first circuit are galliumnitride diodes.

According to an embodiment, in the first circuit, each light-emittingdiode further comprises an emissive layer between the first and secondsemiconductor layers of the diode.

Another embodiment provides a method of manufacturing a display devicesuch as defined hereabove, wherein the forming of the first circuitcomprises the successive steps of:

a) successively depositing, on a surface of a support substrate, avertical stack comprising, in the order from said surface of thesubstrate, the first and second semiconductor layers and a metal layer;

b) forming, from the surface of the stack opposite to the supportsubstrate, trenches crossing said stack across its entire height anddelimiting the different diodes of the first circuit; and

c) forming, in said trenches, a metallization in contact, at the levelof each diode, with the first semiconductor layer of the stack.

According to an embodiment, step b) comprises a first step of partialforming of the trenches down to an intermediate level of the firstsemiconductor layer, followed by a step of deposition of an insulatinglayer on the trench sides, followed by a step of extension of thetrenches down to the lower surface of the first semiconductor layer.

According to an embodiment, the metallization formed at step c) extendsall along height of the trench.

According to an embodiment, the metallization formed at step c) extendsover a portion only of the height of the trenches, up to an intermediatelevel of the first semiconductor layer, the upper portion of thetrenches being filled with an insulating material.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features and advantages, as well as others, will bedescribed in detail in the following description of specific embodimentsgiven by way of illustration and not limitation with reference to theaccompanying drawings, in which:

FIGS. 1A and 1B are cross-section views schematically and partiallyillustrating successive steps of an example of a method of manufacturingan emissive LED display device;

FIGS. 2A and 2B are cross-section views schematically and partiallyillustrating successive steps of an example of a method of manufacturingan emissive LED display device according to an embodiment;

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, and 3G are cross-section viewsillustrating in further detail successive steps of an example of amethod of manufacturing an emissive LED display device according to anembodiment; and

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F are cross-section views illustratingsuccessive steps of another example of a method of manufacturing anemissive LED display device according to an embodiment.

DETAILED DESCRIPTION

The same elements have been designated with the same reference numeralsin the various drawings and, further, the various drawings are not toscale. For the sake of clarity, only the elements that are useful for anunderstanding of the embodiments described herein have been illustratedand described in detail. In particular, the forming of an integrated LEDcontrol circuit has not been detailed, the described embodiments beingcompatible with usual structures and methods of manufacturing of suchcontrol circuits. Further, the composition and the layout of thedifferent layers of an active LED stack have not been detailed, thedescribed embodiments being compatible with usual active LED stacks. Inthe following description, when reference is made to terms qualifyingabsolute positions, such as terms “front”, “rear”, “top”, “bottom”,“left”, “right”, etc., or relative positions, such as terms “above”,“under”, “upper”, “lower”, etc., or to terms qualifying directions, suchas terms “horizontal”, “vertical”, etc., it is referred to theorientation of the drawings, it being understood that, in practice, thedescribed devices and assemblies may be oriented differently. Unlessspecified otherwise, the terms “approximately”, “substantially”, and “inthe order of” signify within 10%, preferably within 5%, of the value inquestion.

FIGS. 1A and 1B are cross-section views partially and schematicallyillustrating successive steps of an example of a method of manufacturingan emissive LED display device.

FIG. 1A illustrates an initial step during which a first integratedcircuit 100 comprising a plurality of LEDs and a second integratedcircuit 150, corresponding to the LED control circuit, are separatelymanufactured.

Circuit 100 comprises a support substrate 101, for example, made ofsapphire, of silicon, of gallium nitride (GaN), or of any other materialon which an active LED stack may be deposited. Circuit 100 furthercomprises a plurality of LEDs 103, for example, identical or similar,arranged on the upper surface of support substrate 101. In top view,LEDs 103 are for example arranged in an array of rows and columns, forexample, regularly distributed on the upper surface of substrate 101.Each LED 103 comprises a vertical stack comprising, in the followingorder from the upper surface of substrate 101, a first dopedsemiconductor layer 105 of a first conductivity type, for example, typeN, an emissive layer 107, and a second doped semiconductor layer 109 ofa second conductivity type, for example, type P. Layers 105 and 109 arefor example made of gallium nitride. Emissive layer 107 is for exampleformed by a stack of one or a plurality of emissive layers, each forminga quantum well, for example, based on GaN, InN, InGaN, AlGaN, AN,AlInGaN, GaP, AlGaP, AlInGaP, or of a combination of one or a pluralityof these materials. As a variation, emissive layer 107 may be anintrinsic gallium nitride layer, that is, it is not intentionally doped.More generally, it will be within the abilities of those skilled in theart to select the material(s) of emissive layer 107 according to thedesired emission wavelength, for example, for an emission in the visiblerange, in the ultraviolet range, or in the infrared range.

In the present example, the lower surface of emissive layer 107 is incontact with the upper surface of layer 105, and the upper surface ofemissive layer 107 is in contact with the lower surface of layer 109. Inpractice, according to the nature of substrate 101, a stack of one or aplurality of buffer layers (not shown) may form an interface betweensupport substrate 101 and semiconductor layer 105.

The elementary LEDs 103 of circuit 100 are separated from one another byvertical trenches extending, in the present example, across the entirethickness of the stack of layers 105, 107, and 109 and emerging onto theupper surface of support substrate 101 or, if present, of the bufferlayer (not shown) separating support substrate 101 from semiconductorlayer 105. More particularly, in this example, the LED separationtrenches form, in top view, a grid such that each mesh of the gridcomprises a single LED 103, and such that each LED 103 is arranged in amesh of the grid.

Circuit 100 comprises, for each LED 103, a metal electrode 111 arrangedon top of and in contact with the upper surface of the semiconductorlayer 109 of the LED. In this example, electrode 111 extends all overthe upper surface of the semiconductor layer 109 of the LED.

Circuit 100 further comprises a metal electrode 113 common to all LEDs103. Electrode 113 extends in the trenches separating LEDs 103 and atthe periphery of the assembly of LEDs 103. In top view, electrode 113forms a continuous grid such that each mesh of the grid contains asingle LED 103 and such that each LED 103 is arranged in a mesh of thegrid. In each LED 103, the lower semiconductor layer 105 of the LED isin contact with common electrode 113. More particularly, in the shownexample, electrode 113 is in contact with a lower portion of the sidesof the semiconductor layer 105 of the LED, all along the periphery ofthe LED. In this example, each LED 103 further comprises, in an upperportion of the LED, a peripheral insulating wall 115, made of adielectric material, in contact, all along the LED periphery, with thesides of the upper electrode 111, of the semiconductor layer 109, and ofthe emissive layer 107 of the LED, as well as with an upper portion ofthe sides of the semiconductor layer 105 of the LED. Peripheralinsulating wall 115 particularly enables to electrically insulateelectrode 113 from electrode 111 and from layers 109 and 107 of the LED.

In the present example, the upper surface of electrode 113, the uppersurfaces of electrode 109, and the upper surfaces of insulating walls115 are substantially at the same level (that is, substantiallycoplanar) and define a substantially planar continuous surface, formingthe connection surface of circuit 100. Thus, the connection surface ofcircuit 100 comprises an alternation of metal regions (electrodes 111and 113) and of dielectric regions (insulating walls 115).

Control circuit 150 is formed inside and on top of a semiconductorsubstrate 151, for example, a silicon substrate. In this example,control circuit 150 comprises, on its upper surface side, for each ofthe LEDs of circuit 100, a metal connection pad 161 intended to beconnected to the electrode 111 of the LED, to be able to control acurrent flowing through the LED and/or to apply a voltage across theLED. Control circuit 150 further comprises, for each LED, connected tothe metal pad 161 dedicated to the LED, an elementary control cell (notdetailed) comprising one or a plurality of transistors, enabling tocontrol the current flowing through the LED and/or a voltage appliedacross the LED. Control circuit 150 is for example made in CMOStechnology.

In the shown example, control circuit 150 further comprises, on itsupper surface side, a metal electrode 163 intended to be connected tothe common electrode 113 of LED circuit 100. Each elementary controlcell of circuit 150 is for example connected to electrode 163.

In the shown example, pads 161 and electrode 163 of integrated circuit150 have, in top view, substantially the same dimensions and the samelayout as the electrodes 111 and 113 of LED circuit 100. In other words,in this example, in top view, electrode 163 forms a continuous grid suchthat each mesh of the grid contains a single pad 161 and such that eachpad 161 is arranged in a mesh of the grid.

Pads 161 are laterally separated from electrode 163 by a ring 165 madeof a dielectric material, for example, silicon oxide. In this example,rings 165 have, in top view, substantially the same dimensions and thesame layout as the insulating walls 115 of circuit 100.

In this example, the upper surface of electrode 163, the upper surfacesof pads 161, and the upper surfaces of insulating rings 165 aresubstantially at the same level (that is, substantially coplanar) andform together a substantially planar continuous surface, forming theconnection surface of circuit 150. Thus, the connection surface ofcircuit 150 comprise an alternation of metal regions (pads 161 andelectrode 163) and of dielectric regions (regions 165), forming apattern identical or similar to the pattern formed by the metal anddielectric regions of the connection surface of circuit 100.

FIG. 1B illustrates a step subsequent to the forming of the circuits 100and 150 of FIG. 1B, during which LED circuit 100 is placed on controlcircuit 150, with its connection surface facing the connection surfaceof control circuit 150. During this step, the connection surface of LEDcircuit 100 (that is, its lower surface in the orientation of FIG. 1B)is bonded to the connection surface of control circuit 150 (that is, itsupper surface in the orientation of FIG. 1B) so that each electrode 111of LED circuit 100 is in mechanical and electric contact with a metalpad 161 of control circuit 150 and so that the common electrode 113 ofLED circuit 100 is in mechanical and electric contact with electrode 163of control circuit 150.

In this example, the connection surface of LED circuit 100 is bonded tothe connection surface of control circuit 150 by direct hybrid bonding,that is, by direct metal-to-metal bonding of the electrodes 111 ofcircuit to the connection pads 161 of circuit 150 and of the electrode113 of circuit 100 to the electrode 163 of circuit 150, and by directdielectric-to-dielectric bonding of the insulating walls 115 of circuit100 to the insulating rings 165 of circuit 150. Direct bonding heremeans a molecular-type bonding, with no addition of adhesive or soldermaterial at the interface between LED circuit 100 and control circuit150.

FIG. 1B further illustrates a step subsequent to the bonding of LEDcircuit 100 to control circuit 150, during which the support substrate101 of LED circuit 100 is removed. While a buffer layer was providedbetween support substrate 101 and the semiconductor layer 105 of LEDcircuit 100, the buffer layer may also be removed during this step, toexpose the surface of semiconductor layer 105 opposite to controlcircuit 150 (that is, its upper surface in the orientation of FIG. 1B).In this example, the display device is indeed intended to emit light onthe side of its surface opposite to control circuit 150, that is, itupper surface in the orientation of FIG. 1B.

The provision of a direct hybrid bonding between LED circuit 100 andcontrol circuit 150 is advantageous in that it enables to obtain aparticularly accurate alignment of LED circuit 100 relative to controlcircuit 150. Indeed, in the case of a direct bonding, once the twocircuits have been aligned, a simple placing into contact of thecircuits is sufficient to set the final position of LED circuit 100relative to control circuit 150. In other words, the bonding isinstantaneous. This is a difference with a bonding with an addition ofmaterial, for example, by soldering, where a compression and/or heatingstep should be implemented after the alignment and the placing intocontact of the two circuits, which may result in a misalignment of thecircuits.

A problem which is posed in the method described in relation with FIGS.1A and 1B is that the rate of occupation of the connection surface ofLED circuit 100 by metal (and accordingly the rate of occupation of theconnection surface of control circuit 150 by metal, the connectionsurfaces of the two circuits being symmetrical) is relatively high,typically greater than 70%, and for example, greater than 80%. Indeed,the connection surface of LED circuit 100 is essentially formed by themetal of the electrodes 111 and 113 of the LEDs, the dielectric materialof insulating walls 115 only occupying a small portion of the connectionsurface.

Further, the distribution of the metal on the connection surface of LEDcircuit 100 (and accordingly the distribution of the metal on theconnection surface of control circuit 150) is not homogeneous. Indeed,as shown in FIGS. 1A and 1B, the metal gate forming the common electrode113 of LED circuit 100 may comprise a relatively wide peripheral frame,for example, having a width (distance between the outer edge and theinner edge of the frame) greater than the pitch between pixels (that is,the center-to-center distance between two neighboring LEDs 103) of thedevice, for example, having a width greater than twice the pitch betweenpixels of the device. As a result, the rate of occupation of theconnection surface of LED circuit 100 by metal is greater at theperiphery of the LED assembly than inside of the LED array.

To obtain a direct hybrid bonding of good quality, it would bepreferable for the occupation rate of the connection surfaces ofcircuits 100 and 150 to be lower, and for the distribution of the metalon the connection surfaces of circuits 100 and 150 to be morehomogeneous. Indeed, prior to the actual bonding step, the connectionsurfaces of circuits 100 and 150 are planarized by chemical-mechanicalpolishing (CMP). The surface evenness obtained during this stepconditions the quality of the direct hybrid bonding of the two circuits.However, to obtain a good surface evenness, it is preferably for therate of occupation of the connection surface by metal to be relativelylow, and for the distribution of the metal on the connection surface tobe as homogeneous as possible.

FIGS. 2A and 2B are cross-section view schematically and partiallyillustrating successive steps of an example of a method of manufacturingan emissive LED display device according to an embodiment.

FIG. 2A illustrates an initial step during which a first integratedcircuit 200 comprising a plurality of LEDs and a second integratedcircuit 250 corresponding to the LED control circuit are separatelymanufactured.

The LED circuit 200 of FIG. 2A comprises the same elements as the LEDcircuit 100 of FIG. 1A, arranged substantially in the same way. Theseelements will not be detailed again hereafter.

The LED circuit 200 of FIG. 2A differs from the LED circuit 100 of FIG.1A mainly in that it further comprises, on its upper surface side, aconnection structure 201, extending over substantially the entiresurface of the circuit.

Connection structure 201 comprises a dielectric layer 203 coating theupper surface of the common electrode 113, of the individual electrodes111, and of the insulating walls 115 of the circuit (corresponding tothe upper surface or connection surface of the circuit 100 of FIG. 1A).As an example, the lower surface of dielectric layer 203 is in contactwith the upper surface of common electrode 113, with the upper surfaceof individual electrodes 111, and with the upper surface of insulatingwalls 115.

Connection structure 201 further comprises a plurality of separateelementary metal connection pads 205, identical or similar, arranged inthrough cavities formed in dielectric layer 203. Connection pads 205extend vertically from the lower surface to the upper surface ofdielectric layer 203. In this example, the upper surface of dielectriclayer 201 and the upper surfaces of metal pads 205 are substantially atthe same level (that is, substantially coplanar) and define asubstantially planar continuous surface, forming the connection surfaceof circuit 200. In this example, the only metal elements visible at theupper surface of connection structure 201 are pads 205. Connection pads205 are regularly distributed over the entire surface of circuit 200. Intop view, connection pads 205 are for example arranged in an array ofrows and columns. As an example, in top view, a same elementary patternformed of a pad 205 surrounded by a portion of dielectric layer 203 isperiodically repeated across the entire upper surface of the circuit, inthe row and column direction of the LED array. As an example, the pitchbetween pixels p1 (that is, the center-to-center distance between twoneighboring pads 205 of connection structure 201) is substantiallyidentical in the row and column direction of the array, and issubstantially identical all over the surface of the array. Preferably,in top view, the rate of occupation of connection structure 201 by themetal pads is in the range from 5 to 50%, for example, in the order of25%.

In each LED 103 of the LED circuit 200 of FIG. 2A, the electrode 111 ofthe LED is in contact, by its upper surface, with the lower surface ofat least one contact pad 205 of connection structure 201. Further, thecommon electrode 1113 of the LED circuit is in contact, at the peripheryof the assembly of LEDs 103, with a plurality of pads 205 of connectionstructure 201. In this example, a same pad 205 of the connectionstructure is only in contact with an electrode 111 or 113 of the LEDcircuit.

In the shown example, the pitch between pads p1 of connection structure201 is shorter than the pitch between pixels p2 of circuit 200, so that,inside of LED assembly 103, the common electrode 113 of the circuit isin contact with the pads 205 of connection structure 201. The describedembodiments are however not limited to this specific case. As a variant,the pitch between pads p1 of connection structure 201 may be equal orsubstantially equal to the pitch between pixels p2 of circuit 200, inwhich case the common electrode 113 of the circuit is in contact withpads 205 only at the periphery of LED assembly 103, and not inside ofLED assembly 103. Each connection pad 205 for example has, in top view,a surface area smaller than the surface area of the electrode 111 of aLED of the circuit. As an example, the pitch between pixels p2 of thecircuit is in the range from 2 to 30 μm, and the width of the elementaryLEDs is in the range from 0.5 to 25 μm.

The control circuit 250 of FIG. 2B is similar to the control circuit 150of FIG. 1B, but for the fact that, in the example of FIG. 2B, theconnection surface of the control circuit is adapted to have the samemetallic and dielectric pattern as the connection surface of LED circuit200.

As an example, the control circuit 250 of FIG. 2B comprises the sameelements as the control circuit 150 of FIG. 1B, arranged substantiallyin the same way, and further comprises, on its upper surface side, aconnection structure 251 similar to the connection structure 201 of LEDcircuit 200, extending over substantially the entire surface of controlcircuit 250.

In particular, connection structure 251 comprises a dielectric layer 253coating the upper surface of the common electrode 163, the individualelectrodes 161, and the insulating rings 165 of the circuit(corresponding to the upper surface or connection surface of the circuit150 of FIG. 1A). As an example, the lower surface of dielectric layer253 is in contact with the upper surface of common electrode 163, withthe upper surface of individual electrodes 161, and with the uppersurface of insulating rings 165.

Connection structure 251 further comprises a plurality of separateelementary metal connection pads 255, identical or similar, arranged inthrough cavities formed in dielectric layer 253. Connection pads 255extend vertically from the lower surface to the upper surface ofdielectric layer 253. In this example, the upper surface of dielectriclayer 251 and the upper surfaces of metal pads 255 are substantially atthe same level (that is, substantially coplanar) and define asubstantially planar continuous surface, forming the connection surfaceof circuit 250. In this example, the only metal elements visible at theupper surface of connection structure 251 are pads 255.

In top view, the dimensions and the distribution of the connection pads255 of the connection structure 251 of control circuit 250 are identicalor similar to the dimensions and to the distribution of the connectionpads 205 of the connection structure 201 of LED circuit 200.

Thus, each pad 161 of the control circuit 250 of FIG. 2A is in contact,by its upper surface, with the lower surface of at least one contact pad255 of connection structure 251. Further, the peripheral portion of thecommon electrode 163 of control circuit 250 is in contact with aplurality of pads 255 of connection structure 251.

FIG. 2B illustrates a step subsequent to the forming of circuits 200 and250 of FIG. 2A, during which LED circuit 200 is placed on controlcircuit 250, with its connection surface facing the connection surfaceof control circuit 250. During this step, the connection surface of LEDcircuit 200 (that is, it lower surface in the orientation of FIG. 2B) isbonded to the connection surface of control circuit 250 (that is, itsupper surface in the orientation of FIG. 2B) so that each connection pad205 of LED circuit 200 is in mechanical and electric contact with aconnection pad 255 of control circuit 250.

In this example, the connection surface of LED circuit 200 is bonded tothe connection surface of control circuit 250 by direct hybrid bonding,that is, by direct metal-to-metal bonding of the connection pads 205 ofcircuit 200 to the connection pads 255 of circuit 250, and by directdielectric-to-dielectric bonding of the dielectric layer 203 of circuit200 to the dielectric layer 253 of circuit 250.

FIG. 2B further illustrates a step subsequent to the bonding of LEDcircuit 200 to control circuit 250, during which the support substrate101 of LED circuit 100 and, possibly, a buffer layer (not shown)provided between substrate 101 and semiconductor layer 105, are removedto expose the surface of semiconductor layer 105 opposite to controlcircuit 250.

An advantage of the embodiment of FIGS. 2A and 2B lies in the provision,on the side of LED circuit 200, of a connection structure 201 and, onthe side of control circuit 250, of a corresponding connection structure251, enabling to obtain, at the level of the connection surfaces of thetwo circuits, a distribution of the metal patterns better adapted to theforming of a direct hybrid bonding of good quality than the distributionimposed, in the example of FIGS. 1A and 1B, by the constraints ofcurrent and/or heat distribution in the LED circuit. In particular,connection structure 201 enables the rate of occupation of theconnection surface of LED circuit 200 (and accordingly the rate ofoccupation of the connection surface of control circuit 250 by metal) tobe smaller than the rate of occupation by metal at the level of theupper surface of metal electrodes 111 and 113 of the LED circuit.Further, connection structure 201 enables the distribution of the metalon the connection surface of LED circuit 200 (and accordingly thedistribution of the metal on the connection surface of control circuit250) to be more homogeneous than the metal distribution at the level ofthe metal electrodes 111 and 113 of the LED circuit.

FIGS. 3A, 3B, 3C, 3D, 3E, 3F, and 3G are cross-section viewsillustrating in further detail successive steps of an example of amethod of manufacturing an emissive LED display screen according to anembodiment. FIGS. 3A, 3B, 3C, 3D, 3E, 3F, and 3G more particularlyillustrate successive steps of an example of a method of manufacturingthe LED circuit 200 described in relation with FIG. 2A.

FIG. 3A illustrates a step during which semiconductor layer 105,emissive layer 107, and semiconductor layer 109 are successivelydeposited on the upper surface of support substrate 101, forming anactive LED stack. At this stage, layers 105, 107, and 109 continuouslyextend over substantially the entire upper surface of support substrate101. Layers 105, 107, and 109 are for example deposited by epitaxy onthe upper surface of support substrate 101. In practice, according tothe nature of substrate 101, a stack of one or a plurality of bufferlayers (not shown) may form an interface between support substrate 101and lower semiconductor layer 105.

FIG. 3A further illustrates a step of deposition, on top of and incontact with the upper surface of semiconductor layer 109, of a metallayer 111 forming an upper electrode of the active LED stack. In thisexample, metal layer 111 is continuously deposited over substantiallythe entire upper surface of layer 109. Metal layer 111 is for exampledeposited by physical vapor deposition (PVD). As an example, metal layer111 is made of copper or of titanium.

FIG. 3B illustrates a step of forming of trenches 301 extendingvertically in the stack of layers obtained at the end of the steps ofFIG. 3A, from the upper surface of the stack, that is, from the uppersurface of metal layer 111. Trenches 301 thoroughly cross layers 111,109, and 107 and are interrupted at an intermediate level of lowersemiconductor layer 105. In top view, trenches 301 form a continuousgrid delimiting the different LEDs 103 of the circuit.

FIG. 3C illustrates a step of deposition of a dielectric layer 115, forexample, made of silicon oxide, all over the upper surface of thestructure obtained at the end of the steps of FIGS. 3A and 3B, that is,on the sides and on the bottom of trenches 301 and on the upper surfaceof the upper electrodes 111 of LEDs 103. Layer 115 is preferablydeposited by a conformal deposition method, for example, by atomic layerdeposition (ALD). As an example, the thickness of insulating layer 115is in the range from 10 nm to 1 μm.

FIG. 3D illustrates a step of removal of dielectric layer 115 from thebottom of trenches 301 and the upper surface of the electrodes 111 ofLEDs 103. During this step, layer 115 is kept on the lateral walls oftrenches 301. For this purpose, layer 115 is for example etched byvertical anisotropic etching.

FIG. 3D further illustrates a step of removal, by etching, of theportions of semiconductor layer 105 located at the bottom of trenches301, to continue trenches 301 down to the upper surface of substrate101, or possibly down to the upper surface of the buffer layer formingan interface between substrate 101 and semiconductor layer 105. At theend of this step, the different LEDs 103 are totally electricallyinsulated from one another by trenches 301.

FIG. 3E illustrates a step of deposition of a metallization 113, forexample, made of copper or of titanium, on the lateral walls and on thebottom of the trenches 301 obtained at the end of the steps of FIG. 3D.In the shown example, metallization 113 entirely fills trenches 301. Asan example, metallization 113 is formed by a damascene-type method,comprising a step of deposition of a metal layer over the entire uppersurface of the assembly, with a thickness sufficient to fill trenches301, followed by a step of chemical-mechanical polishing of the uppersurface of the assembly to planarize the upper surface of the device andremove the portions of the metal layer topping LEDs 103, to expose theupper surface of insulating walls 115 (to insulate common electrode 113from electrodes 111).

FIG. 3F illustrates a step of deposition of the dielectric layer 203 ofconnection structure 201, on top of and in contact with the uppersurface of the structure obtained at the end of the step of FIG. 3E.Dielectric layer 203 is for example made of silicon oxide or of siliconnitride. Layer 203 is for example deposited by chemical vapor deposition(CVD) or by any other adapted deposition method. Dielectric layer 203 isinitially continuously deposited over substantially the entire uppersurface of the structure obtained at the end of the steps of FIG. 3E,that is, on the upper surface of electrodes 113 and 111 and on the uppersurface of the insulating walls 115 of the circuit.

FIG. 3F further illustrates a step of local etching of dielectric layer203, to form in layer 203 through openings 303 emerging onto the uppersurfaces of electrodes 111 and 113 and intended to contain theconnection pads 205 of connection structure 201.

FIG. 3G illustrates a step of filling of openings 303 with metal, forexample, titanium or copper, to form the connection pads 205 ofconnection structure 201. As an example, connection pads 205 are formedby a damascene-type method, comprising a step of deposition of a metallayer over the entire upper surface of the structure obtained at the endof the steps of FIG. 3F, across a thickness sufficient to fill openings303, followed by a step of chemical-mechanical polishing of the uppersurface of the structure to planarize the upper surface of the circuitand remove the portions of the metal layer topping dielectric layer 203between openings 303, to insulate connection pads 205 from one another.

At the end of this step, a LED circuit 200 identical or similar to thatof FIG. 2A, having a substantially planar upper surface or connectionsurface comprising an alternation of metal regions (pads 205) and ofdielectric regions (the portions of layer 203 laterally surrounding pads205) is obtained.

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F are cross-section views illustratingsuccessive steps of another example of a method of manufacturing anemissive LED device according to an embodiment. FIGS. 4A, 4B, 4C, 4D,4E, and 4F more particularly illustrates successive steps of an exampleof a method of manufacturing an alternative embodiment of the LEDcircuit 200 described in relation with FIG. 2A.

FIG. 4A illustrates a step identical or similar to the step described inrelation with FIG. 3A, during which are successively deposited, on theupper surface of support substrate 101, semiconductor layer 105,emissive layer 107, and semiconductor layer 109, forming an active LEDstack, and then metal electrode layer 111 on top of and in contact withthe upper surface of semiconductor layer 109.

FIG. 4B illustrates a step of forming of trenches 401 verticallyextending in the stack of layers obtained at the end of the steps ofFIG. 4A, from the upper surface of the stack, that is, from the uppersurface of metal layer 111. In this example, trenches 401 thoroughlycross layers 111, 109, 107, 105 and are interrupted on the upper surfaceof support substrate 101, or, possibly, on the upper surface of a bufferlayer forming an interface between substrate 101 and semiconductor layer105. In top view, trenches 401 form a continuous grid delimiting thedifferent LEDs 103 of the circuit. It should be noted that, in thisexample, the steps of forming of a peripheral insulating wall 115 in theupper portion of LEDs 103, described in relation with FIGS. 3B, 3C, and3D, are not provided. Thus, at the end of the trench forming step ofFIG. 4B, the sides of layers 111, 109, 107, and 105 of the LEDs areexposed all along their height.

FIG. 4C illustrates a step of partial filling of trenches 401 with ametal layer 403. More particularly, in the present example, metal layer403 fills the bottom of the trenches, up to a level lower than the uppersurface of semiconductor layer 105. In other words, in each LED 103,metal layer 403 is in contact with a lower portion of the sides of thesemiconductor layer 105 of the LED, all along the periphery of the LED.Metal layer 403 is however not in contact with the upper portion of thesides of layer 105, nor with the sides of the layers 107, 109, and 111of LEDs 103.

FIG. 4D illustrates a step during which trenches 401 are finally filledwith an insulating material 405, for example, silicon oxide. As anexample, a layer of insulating material 405 is deposited all over theupper surface of the structure obtained at the end of the steps of FIG.4C, that is, on top and in contact with the upper surface of metal layer403, on top of and in contact with the upper portion of the sides oflayer 105 and the sides of the layers 107, 109, and 111 of LEDs 103, andon top of and in contact with the upper surface of the electrodes 111 ofLEDs 103. As an example, the layer of material 405 is deposited across athickness greater than the depth of the upper portion of trenches 401which is not filled with metal layer 403, to entirely fill trenches 401,after which a chemical-mechanical polishing step is implemented toplanarize the upper surface of the structure and expose the uppersurface of the electrodes 111 of LEDs 103.

FIG. 4E illustrates a step of electric contacting on metal layer 403.For this purpose, a through opening emerging onto the upper surface ofmetal layer 413, for example, at the periphery of the assembly of LEDs103 of the circuit, is first formed in insulating layer 405, from itsupper surface. The opening is then filled with a metal 407, for example,by a damascene-type method, to transfer the contact at the level of theupper surface of circuit. In the shown example, contacting metallization407 is arranged at the periphery of the assembly of LEDs 103 and totallysurrounds the assembly of LEDs 103 but does not extend into the assemblyof LEDs 103. As a variant, contacting metallization 407 may have agrid-shaped pattern, similar to that of metal layer 403, extending notonly at the periphery of the assembly of LEDs 103 but also into theassembly of LEDs 103, between neighboring LEDs of the circuit. At theend of this step, metallizations 403 and 407 define the common electrode113 of the LED circuit.

FIG. 4F illustrates a step of deposition of dielectric layer 203 ofconnection structure 201, on top of and in contact with the uppersurface of the structure obtained at the end of the steps of FIG. 4E,and then of forming of metal connection pads 205 in dielectric layer203, similarly to what has been described in relation with FIGS. 3F and3G (forming of through openings emerging onto the upper surfaces ofmetallizations 111 and 407, and filling of the openings with metal toform pads 205).

At the end of this step, a LED circuit 200′ similar to the circuit 200of FIG. 2A is obtained, with the difference that, in circuit 200′, aninsulator 405 thicker than the peripheral insulating walls 115 ofcircuit 200 separates LEDs 103 from one another.

Specific embodiments have been described. Various alterations,modifications, and improvements will occur to those skilled in the art.In particular, the described embodiments are not limited to theabove-described specific example where the LEDs of the device are basedon gallium nitride. More generally, the described embodiments may beapplied to any other LED technology.

The invention claimed is:
 1. A display device comprising a firstintegrated circuit comprising: an assembly of a plurality oflight-emitting diodes, each diode comprising a vertical stack of a firstsemiconductor layer of a first conductivity type and of a secondsemiconductor layer of the second conductivity type, and the diodesbeing separated from one another by trenches; for each diode, a firstelectrode arranged on top of and in contact with the surface of thesecond layer opposite to the first layer; a second electrode common tosaid plurality of diodes, the second electrode extending in the trenchesand at the periphery of the plurality of diodes and being in contact, ineach diode, with the first semiconductor layer; and on the side of asurface of the first circuit opposite to the first semiconductor layer,a connection structure comprising a dielectric layer having a pluralityof identical or similar connection pads, regularly distributed acrossthe entire surface of the first circuit, arranged therein, each diodehaving its first electrode in contact with at least one pad of theconnection structure, and the second electrode being in contact with aplurality of pads of the connection structure at the periphery of theplurality of diodes.
 2. The device according to claim 1, furthercomprising a second integrated circuit formed inside and on top of asemiconductor substrate, the second circuit comprising, for each diodeof the first circuit, a metal pad intended to be connected to the firstelectrode of the diode, and a metal electrode intended to be connectedto the second electrode of the first circuit.
 3. The device according toclaim 2, wherein the first and second circuits are bonded to each otherby direct hybrid bonding so that each first electrode of the firstcircuit is electrically connected to a metal pad of the second circuitand so that the second electrode of the first circuit is electricallyconnected to the electrode of the second circuit.
 4. The deviceaccording to claim 2, wherein the second circuit comprises a connectionstructure comprising a dielectric layer having a plurality of identicalor similar connection pads, regularly distributed across the entiresurface of the second circuit, arranged therein, each metal pad of thesecond circuit being in contact with at least one connection pad of theconnection structure of the second circuit, and the electrode of thesecond circuit being in contact with a plurality of connection pads ofthe connection structure of the second circuit in a peripheral region ofthe electrode of the second circuit.
 5. The device according to claim 2,wherein the second circuit comprises, for each metal pad of the secondcircuit, an elementary control cell comprising one or a plurality oftransistors, enabling to control the current flowing through thecorresponding diode of the first circuit and/or a voltage applied acrossthe corresponding diode of the first circuit.
 6. The device according toclaim 2, wherein the second circuit is made in CMOS technology.
 7. Thedevice according to claim 1, wherein the diodes of the first circuit aregallium nitride diodes.
 8. The device according to claim 1, wherein, inthe first circuit, each light-emitting diode further comprises anemissive layer between the first and second semiconductor layers of thediode.
 9. The device according to claim 1, wherein the pitch betweenpixels of the connection structure of the first integrated circuit isshorter than the pitch between diodes of the first integrated circuit,so that, within the diode assembly of the first integrated circuit, thesecond electrode common to said plurality of diodes is in contact withpads of the connection structure of the first integrated circuit. 10.The device according to claim 1, wherein the pads of the connectionstructure of the first integrated circuit are arranged in an array ofrows and columns, according to a substantially constant pitch betweenpixels in the row and column direction of the array.
 11. The deviceaccording to claim 1, wherein the connection pads of the connectionstructure of the first integrated circuit are arranged in throughcavities formed in the dielectric layer of the connection structure ofthe first integrated circuit.
 12. A method of manufacturing the displaydevice according to claim 1, wherein the forming of the first circuitcomprises the successive steps of: a) successively depositing, on asurface of a support substrate, a vertical stack comprising, in theorder from said upper surface of the substrate, the first and secondsemiconductor layers and a metal layer; b) forming, from the surface ofthe stack opposite to the support substrate, trenches crossing saidstack across its entire height and delimiting the different diodes ofthe first circuit; and c) forming, in said trenches, a metallization incontact, at the level of each diode, with the first semiconductor layerof the stack.
 13. The method according to claim 12, wherein step b)comprises a first step of partial forming of the trenches down to anintermediate level of the first semiconductor layer, followed by a stepof deposition of an insulating layer on the sides of the trenches,followed by a step of extension of the trenches down to the lowersurface of the first semiconductor layer.
 14. The method according toclaim 13, wherein the metallization formed at step c) extends all alongthe height of the trench.
 15. The method according to claim 12, whereinthe metallization formed at step c) extends along a portion only of theheight of the trenches, up to an intermediate level of the firstsemiconductor layer, the upper portion of the trenches being filled withan insulating material.